(Diene)iron tricarbonyl

In organometallic chemistry, (diene)iron tricarbonyl describes a diverse family of related coordination complexes consisting of a diene ligand coordinated to a Fe(CO)3 center. Often the diene is conjugated, e.g., butadiene, but the family includes nonconjugated dienes as well. The compounds are yellow, air-stable, often low-melting, and soluble in hydrocarbon solvents. The motif is so robust that even unstable dienes form easily characterized derivatives, such as norbornadienone and cyclobutadiene.

Scope

The inventory of complexes is large, and has been extended to steroidal and terpenoid substrates.

Selected (diene)Fe(CO)3 Complexes
dieneCAS RNnotes
norbornadiene12307-07-2liquid, -2 °C[1]
1,5-Cyclooctadiene12093-20-8see [2]
1,3-Cyclooctadiene33270-50-7One of two isomers of (cyclooctadiene)Fe(CO)3[3]
1,3-Butadiene12078-32-919 °C, see (Butadiene)iron tricarbonyl
Isoprene32731-93-4liquid at RT, chiral[4]

Preparation

Many of diene complexes were originally prepared by reaction of iron pentacarbonyl with the diene in refluxing toluene or similar solvents. Often yields are modest because the complexes, which are often liquids, volatilize during workup.[1] Especially for thermally sensitive derivatives, displacement of bda from (Benzylideneacetone)iron tricarbonyl (Fe(bda)(CO)3) has been recommended.[5]

Characterization

IR spectra of these complexes show nCO bands at 2040 and 1969. At low temperatures, the lower energy band splits, which has been interpreted as evidence for fluxionality on the IR timescale.[6]

Reactions

The Fe(CO)3 unit serves as a protecting group for the diene, preventing the diene from participating in Diels-Alder reactions and hydrogenation. The diene is usually deprotected with ceric ammonium nitrate.[7]

References
  1. Green, M. L. H.; Pratt, L.; Wilkinson, G. (1960). "206. Spectroscopic studies of some organoiron complexes". Journal of the Chemical Society (Resumed): 989. doi:10.1039/JR9600000989.
  2. Kruczynski, Leonard.; Takats, Josef. (1976). "Intramolecular rearrangement in (.eta.-diene)tricarbonyliron and -ruthenium compounds. A carbon-13 nuclear magnetic resonance study". Inorganic Chemistry. 15 (12): 3140–3147. doi:10.1021/ic50166a041.
  3. Lewis, J.; Cotton, F. A.; Deeming, A. J.; Josty, P. L.; Ullah, S. S.; Domingos, A. J. P.; Johnson, B. F. G. (1971). "Tricarbonyl(cyclooctadiene) complexes of iron(0), ruthenium(0), and osmium(0)". Journal of the American Chemical Society. 93 (18): 4624–4626. doi:10.1021/ja00747a066.
  4. King, R.B.; Manuel, T.A.; Stone, F.G.A. (1961). "Chemistry of the metal carbonyls—IX". Journal of Inorganic and Nuclear Chemistry. 16 (3–4): 233–239. doi:10.1016/0022-1902(61)80495-8.
  5. Domingos, A. J. P.; Howell, J. A. S.; Johnson, B. F. G.; Lewis, J. (1990). Reagents for the Synthesis of η-Diene Complexes of Tricarbonnyliron and Tricarbonylruthenium. Inorganic Syntheses. pp. 52–55. doi:10.1002/9780470132593.ch11. ISBN 9780470132593.
  6. Turner, James J.; Bühl, Michael (2018). "Infrared Dynamics of Iron Carbonyl Diene Complexes". The Journal of Physical Chemistry A. 122 (14): 3497–3505. doi:10.1021/acs.jpca.7b12309. hdl:10023/16989. PMID 29394061.
  7. Donaldson, William A.; Chaudhury, Subhabrata (2009). "Recent Applications of Acyclic (Diene)iron Complexes and (Dienyl)iron Cations in Organic Synthesis". European Journal of Organic Chemistry. 2009 (23): 3831–3843. doi:10.1002/ejoc.200900141. PMC 3121309. PMID 21709767.
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